This is a very bad idea.

A counting semaphore is fundamentally the wrong mechanism(*) for watermarking a queue; so futzing with the API of a counting semaphore to allow it to be used (badly) for this purpose is just all kinds of wrong.

(*)In brief, A counting semaphore is designed for controlling concurrent access to a resource that is limited but has multiple instantiations.

A queue, even a pre-limited queue, does not fit this criteria.

  1. a queue can only be accessed by one user (reader or writer) at a time, regardless of how much is does or can contain.
  2. the availability of a queues resources is not determined by the actions of competing consumers -- the reason d'etre of the counting semaphore -- but rather by the actions of the producer.

    They are very different animals.

  3. Having the consumer(s) of a queue effectively control the producer(s) for that queue, requires multi-way synchronisation, and defeats the primary purpose of the queue: that of acting as a flexible buffer between producers and consumers to avoid the need for and problems associated with such synchronisation.

    Those problems include:

    Consumers and producers can become 'step-locked'.

    The flow falls into a pattern of the consumer(s) all wasting many time-slices (and expensive context switches) waiting for the producer(s). Then alternately, the producer(s) all waste time-slices waiting for the consumer(s). The flow becomes lock-stepped wasting many context switches between each forward step.

    The very purpose of queues is to alleviate this problem by acting as a flexible buffer removing the need for synchronisation.

See 940030 for a little more discussion.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

In reply to Re^2: Boolean Thread::Semaphore ? by BrowserUk
in thread Boolean Thread::Semaphore ? by chrestomanci

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